A fuel injector is used to inject fuel into a combustion chamber of a diesel engine. A tip of the fuel injector has a number of small nozzles defined therein. Pressurized fuel is advanced from the fuel injector, through the nozzles and into the combustion chamber of the diesel engine. These nozzles must be formed so that a precise amount of fuel is advanced through the fuel injector tip into the combustion chamber. This precise metering allows the fuel to be evenly distributed in the combustion chamber.
Wire electric discharge machining (WEDM) has been used to form nozzles in the tip of the fuel injector. WEDM directs an electrical charge through the material in the tip of the fuel injector to form a hole in the tip of the fuel injector. WEDM produces small straight holes which are ideal for use as nozzles. However, a drawback of using WEDM is that WEDM can only form nozzles with a diameter greater than approximately 150 microns. In addition, the WEDM process takes a relatively long time to form a nozzle in the tip of the fuel injector.
Electronic engine controls rapidly adjust the amount of fuel injected into the combustion chamber via the fuel injector. In order to increase the speed that the fuel as it is injected into the combustion chamber, the pressure of the fuel must be increased. To increase the pressure of the fuel, the diameter of the nozzle must correspondingly be decreased. The fuel pressures currently being used require nozzles with diameters smaller than the minimum diameter that can be produced using WEDM.
Laser drilling can produce a nozzle with a smaller diameter than nozzles produces with WEDM. The beam of a laser can be focused on a precise area of the tip of the fuel injector to produce very small holes, on the order of twenty microns in diameter. In fact, the focused laser beam can produce a hole with a diameter much smaller than the diameter required for the nozzle in the tip of the fuel injector.
A process known as trepanning, or circular interpolation drilling, can be used to produce a hole with a diameter larger than the diameter of the focused laser beam. In the trepanning process, the laser beam is moved along the perimeter of a circle or other shape. Moving the laser beam around the perimeter of the circle forms a nozzle with the diameter equal to the diameter of the circle. The trepanning process allows a nozzle with a diameter of approximately one hundred and fifty microns to be formed with a focused laser beam that produces holes with a diameter of approximately twenty microns.
However, a drawback to using the trepanning process is that a waste product, known as slag or dross, is deposited around an outer surface of the nozzle as the nozzle is formed. As the laser beam cuts through the material in the tip of the fuel injector, the waste product, consisting of molten metal and other impurities, is deposited around the periphery of the nozzle. During operation of the diesel engine, the deposited waste product disturbs the flow of fuel being advanced through the nozzle into the combustion chamber. Disturbance of the flow of fuel causes an uneven distribution of the fuel in the combustion chamber which can degrade performance of the diesel engine.
What is needed therefore is an apparatus and method for laser drilling a nozzle in the tip of a fuel injector which overcomes one or more of the above-mentioned drawbacks.